Over the years, many electronic instruments and devices and been sufficiently reduced in size to become portable, and in turn, small enough to be held and operated in the hand of the user. The advent of integrated circuits greatly increased the number of devices that could achieve portability and handheld status, as well as increasing the functionality of such devices.
Earlier handheld devices such as measuring instruments or electronic calculators had minimal requirements for display capability and much of the available area on the package of the device was dedicated to controls such as knobs and buttons, or a keypad. For such instruments, a display capable of handling up to a dozen or so alphanumeric characters was sufficient.
As the information processing capabilities of handheld devices have grown, the types of information and data that can be displayed thereon has expanded. For electronic calculators, alphanumeric displays have been supplemented by displays that are capable of graphically representing mathematical functions.
As handheld calculators acquired more sophisticated display capabilities, they have evolved into palmtop computer systems that provide text processing and communications applications. Palmtop computer systems are commonly used to implement various Personal Information Management (PIM) applications such as an address book, a daily organizer, and electronic notepads.
The competing interests of increasing functionality and small size in handheld devices have led to the adoption of touch panel displays that provide a shared surface for input and output functions. Touch panel displays are typically multilayer structures combining a transparent means of sensing the position and possibly the magnitude of a contact local to the display surface with an underlying display.
Most touch panel displays use an electronic means of sensing input; analog-resistive, matrix-resistive, capacitive and near field imaging (NFI) are examples of current technologies. Depending upon the technology used, a touch panel may require several distinct electrical connections to accommodate drive and sense signals to one or more transparent electrode layers.
Touch panel displays are extremely versatile in that a limitless variety of “virtual buttons” can be displayed for user input. A palmtop computer employing a touch panel display can easily modify the areas of the display dedicated to input and output in response to the immediate requirements of the user and the application. Thus, for handheld devices that incorporate a touch panel display, it is desirable to maximize the usable area of the display within the size constraint of being handheld. Further, since not all hands are of the same size, there is a general rule that smaller is better and this applies to width and length as well as height. Ideally, the difference in width and length between the touch panel display and the underlying structure of the handheld device is kept to a minimum.
In spite of the fact that it is desirable to maximize the area available for touch panel displays, a portion of the perimeter of typical touch panel displays used in handheld devices is lost due to the manner in which they are integrated into the handheld device.
For instance, a bezel or faceplate is commonly used to hold the touch panel in place and mask its perimeter. The mechanical function of securing the touch panel in place is relatively straightforward. The second function of a bezel is less than obvious in that its purpose is hidden by design. The sensing portion of touch panel displays typically has a non-transparent electrical structure on its perimeter that includes conductive traces and insulation between layers. The geometry and coloration of the conductive and dielectric materials are such that they are typically visually non-homogeneous and require masking by the bezel.
Aesthetics aside, it is desirable to have a neutral, homogeneous perimeter surrounding the touch panel display to minimize visual distraction from the display itself. Due to the limited display size and the variety of environments in which a handheld device may be used, it is important to give the user every assistance in viewing the display. In typical handheld devices, a bezel achieves the desired homogeneous perimeter by hiding the non-homogeneous pattern beneath it. However, the use of a bezel dictates an unwanted increase in the overall thickness of the handheld device over that which could be obtained for a flush-mounted touch panel display, and may also contribute to an increase in the length and width as well.
Thus, a need exists for a touch panel display that can be integrated into a handheld device without requiring a bezel and its associated increase in overall device dimensions. There is also a need for a flush mounted touch panel display that presents a visually homogeneous border to the user without the use of a bezel.